When a shock is applied externally to the side of the vehicle due to a side impact or the like, the vehicle door or the vehicle structure may be deformed by the impact force depending on the magnitude of the shock. In order to relax the shock force to the passenger due to the deformation, various types of air bag are proposed which are inflated between the lateral face and the passenger when a side impact occurs, so that the shock force exerted on the passenger is absorbed by the air bag (e.g. Japanese Patent Laid-open Publication (OPI) 4-50052, Japanese OPI 4-356246, and so on).
A heretofore proposed side impact air bag system has an air bag folded up together with a gas generating device, both installed inside a vehicle seat (mainly in the seat back) to maintain the relative position to the passenger in a constant value, and is provided with detection means for detecting a side impact to blow the gas from the gas generating device. The air bag is provided with a vent hole for exhausting the gas from the bag after inflation, and an appropriate pressure for absorbing the shock is obtained by the vent hole. The vent hole is formed at a position for even gas exhaustion so that vibration at inflation is prevented and the air bag is uniformly inflated, for example, at a position symmetrical in the vertical direction when the air bag is inflated.
When a side impact is detected by the detection means, gas is instantaneously blown out from the gas generating device into the air bag to inflate the air bag towards the front side of the vehicle so that the air bag is present between the side of the vehicle and the passenger. Gas is discharged from the vent hole according to the load of door and the like deformed by the side impact to obtain an appropriate pressure to absorb the shock so that the shock to the passenger is absorbed to protect the passenger.
The conventional side impact air bag system is provided with a vent hole to obtain an adequate pressure for absorbing the shock. However, since the vent hole in the conventional air bag is formed at positions and in number in consideration of preventing vibration or the like during inflation, it has a problem that gas discharge becomes inappropriate and the desired internal pressure and inflation cannot be obtained. That is, if the gas discharge is too fast, the air bag cannot be positively inflated in a small space between the vehicle body and the passenger. Further, there is a danger that the vent hole is closed by a door trim or the like during inflation, gas discharge becomes insufficient, the desired internal pressure is not obtained, and an appropriate pressure for absorbing the shock is not obtained. That is, if the pressure in the air bag is too high, a shock to the passenger due to the pressure of air bag inflation is too high, thus the shock cannot be absorbed.
With a view to eliminate the above prior art problems, a primary object of the present invention is to provide a side impact air bag system which can always provide a desired internal pressure and an inflation condition.